Craniofacial growth in untreated skeletal Class I subjects with low, average, and high MP-SN angles: a longitudinal study.

Sixty-eight (36 male and 32 female) untreated skeletal Class I subjects with low (< or = 27 degrees ), average (>27 degrees - <37 degrees ), and high (> or = 37 degrees ) mandibular plane (MP-SN) angles were selected from the Bolton-Brush and Burlington Growth Studies. Cephalograms of each subject at ages 9 and 18 were traced, and 28 parameters were measured. The difference in each parameter from ages 9 to 18 was calculated, and comparisons were made between the groups with low, average, and high angles. Results showed that, for boys and girls at age 9, the low-angle groups exhibited significantly larger SNA angle, SNB angle, facial taper, PFH, PFH:AFH, and ramus height, and the high-angle groups showed significantly larger ANS-Me and gonial angle. From ages 9 to 18, all the male and female low-, average-, and high-angle groups showed an increase in SNA and SNB angles, and PFH:AFH, and a decrease in ANB angle, convexity (more flattened face), MP-SN angle, and gonial angle (mandibular forward rotation). The dental measurements showed few changes with growth in all groups. In terms of skeletal measurements from ages 9 to 18, similar growth changes were found between the sexes in most angular measurements, but males had larger values in linear measurements than females.